1. Field of the Invention
The present invention relates generally to water treatment, and more particularly to a membrane filtration apparatus which is equipped with a cleaning device to clean the membranes thereof.
2. Description of the Related Art
Water is one of the essential elements to maintain life, and it is indispensable to the modern industry also. The demand of industrial water is much higher than ever, so that the pollution prevention and reuse of industrial wastewater becomes more and more important.
In the past time, the industrial wastewater should be properly treated before discharge. The treatments process units include aeration, sedimentation, filtration, chemical coagulation, activated carbon treatment, and biological treatment, etc. The governments have many regulations to limit the industrial wastewater discharge, in order to reduce environmental impact.
Recently, due to the extreme climate, water exhaustion condition is getting worse, so that the shortage of water resource becomes a serious problem. Therefore, how to recycle the industrial water is a new issue in the modern wastewater treatment.
Membrane bioreactor (MBR) is a new developed technique of wastewater treatment in the present days, and it is an optimal process for wastewater reuse. MBR is the combination of a membrane process, like microfiltration or ultrafiltration, with a suspended growth bioreactor. It provides micropores on the membrane to restrict activated sludge of aerobic or anaerobic system in the reactor. Typically, MBR is applied in the secondary biological treatment, and it has the performance of the tertiary treatment because of its combination of membrane and biological process.
FIG. 1 shows a membrane filtration module 104 of a MBR system, which includes a frame 106, which is divided into an aeration area at a low section and a membrane area at an up section, an aeration device 108 mounted in the aeration area of the frame 106, and a plurality of membrane members 116 mounted in the membrane area of the frame 106. The aeration device 108 includes a main pipe 110 and several branch pipes 112. Each branch pipe 112 is provided with several apertures 114. An air blower (not shown) is connected to the main pipe 110 to provide compressed air, and the compressed air will go out of the aeration device 108 via the apertures 114. Each membrane member 116 is connected to a permeate pipe 118 and a common water pipe 120. As shown in FIG. 2, the membrane member 116 has a frame board 122, to opposite sides of which membranes 124 are attached. The frame board 122 is hollow and has an outlet 126 on a top thereof. The permeate pipe 118 is connected to the outlet 126.
Typically, a plurality of the membrane filtration apparatuses 104 are mounted in a sewage tank (not shown). Sewage flows into the membrane members 116 through the membranes 124 and is filtered through the micropores on the membranes. The permeated clean water flows into the common water pipe 120 through the outlets 126 of the frame boards 122 and the permeate pipes 118 for the next process.
Inevitably, there is sludge attached to the membranes 124 after the sewage flows there through. The aeration device 108 provides air bubbles to remove the sludge from the membranes 124. Theoretically, the sludge should be removed by the air bubbles. However, a crosslink reaction may happen in the sludge and the product is very hard to remove. Besides, the interval spaces between the membrane members 116 are very narrow (about 8 mm) so that they are very easy to be jammed by the sludge after a time of operation. Therefore, the operator has to add a cleaning solution into the membrane filtration apparatuses 104 to periodically remove the sludge, and sometimes it even has to take the membrane members 116 out of the frame 106 to wash the membranes 124 directly.